Vulnerability in JSON Parser in Ruby on Rails 3.0 and 2.3

There is a vulnerability in the JSON code for Ruby on Rails which
allows attackers to bypass authentication systems, inject arbitrary
SQL, inject and execute arbitrary code, or perform a DoS attack on a
Rails application. This vulnerability has been assigned the CVE
identifier CVE-2013-0333.

Impact
- ------
The JSON Parsing code in Rails 2.3 and 3.0 support multiple parsing
backends. One of the backends involves transforming the JSON into
YAML, and passing that through the YAML parser. Using a specially
crafted payload attackers can trick the backend into decoding a subset
of YAML.

All users running an affected application should upgrade or use the
workaround immediately.

Note: This is a separate vulnerability to CVE-2013-0156, if you are
running a 2.3 or 3.0 application you must still take action to protect
your application.

Releases
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The 3.0.20 and 2.3.16 releases are available at the normal locations.

Workarounds
- -----------
If you are unable to upgrade, or apply the patches, you can work
around this vulnerability by switching backends to the JSONGem
backend. Place this code in an application initializer:

ActiveSupport::JSON.backend = "JSONGem"

If you are running Ruby 1.8 you will need to ensure that the `json` or
`json_pure` gems are installed and in your application's Gemfile.
Ruby 1.9 includes this code already.

Patches
- -------
To aid users who aren't able to upgrade immediately we have provided
patches for the two supported release series. They are in git-am
format and consist of a single changeset.

Please note that only the 2.3.x, 3.1.x and 3.2.x series are supported
at present. Users of earlier unsupported releases are advised to
upgrade as soon as possible as we cannot guarantee the continued
availability of security fixes for unsupported releases.

Credits
- -------

Thanks to Lawrence Pit of Mirror42 for discovering the vulnerability
and working closely with us to ensure we shipped a comprehensive fix.
Thanks also to the RedHat security response team for helping us with
regression testing.